The harvesting of wild seafood is usually known as fishing or hunting, and the cultivation and farming of seafood is known as aquaculture, or fish farming in the case of fish. Seafood is often distinguished from meat, although it is still animal and is excluded in a vegetarian diet. Seafood is an important source of protein in many diets around the world, especially in coastal areas.

Most of the seafood harvest is consumed by humans, but a significant proportion is used as fish food to farm other fish or rear farm animals. Some seafoods (kelp) are used as food for other plants (fertilizer). In these ways, seafoods are indirectly used to produce further food for human consumption. Products, such as oil and spirulina tablets, are also extracted from seafoods. Some seafood is fed to aquarium fish, or used to feed domestic pets, such as cats. A small proportion is used in medicine, or is used industrially for non-food purposes (leather).

Various foods depicted in an Egyptian burial chamber, including fish, c. 1400 BCE.

The harvesting, processing, and consuming of seafoods are ancient practices with archaeological evidence dating back well into the Paleolithic.[1][2] Findings in a sea cave at Pinnacle Point in South Africa indicate Homo sapiens (modern humans) harvested marine life as early as 165,000 years ago,[1] while the Neanderthals, an extinct human species contemporary with early Homo sapiens, appear to have been eating seafood at sites along the Mediterranean coast beginning around the same time.[3] Isotopic analysis of the skeletal remains of Tianyuan man, a 40,000-year-old anatomically modern human from eastern Asia, has shown that he regularly consumed freshwater fish.[4][5]Archaeology features such as shell middens,[6] discarded fish bones and cave paintings show that sea foods were important for survival and consumed in significant quantities. During this period, most people lived a hunter-gatherer lifestyle and were, of necessity, constantly on the move. However, where there are early examples of permanent settlements (though not necessarily permanently occupied) such as those at Lepenski Vir, they are almost always associated with fishing as a major source of food.

The ancient riverNile was full of fish; fresh and dried fish were a staple food for much of the population.[7] The Egyptians had implements and methods for fishing and these are illustrated in tomb scenes, drawings, and papyrus documents. Some representations hint at fishing being pursued as a pastime.

World fisheries harvest, both wild and farmed, in million tonnes, 1950–2010[8]

Fishing scenes are rarely represented in ancient Greek culture, a reflection of the low social status of fishing. However, Oppian of Corycus, a Greek author wrote a major treatise on sea fishing, the Halieulica or Halieutika, composed between 177 and 180. This is the earliest such work to have survived to the modern day. The consumption of fish varied in accordance with the wealth and location of the household. In the Greek islands and on the coast, fresh fish and seafood (squid, octopus, and shellfish) were common. They were eaten locally but more often transported inland. Sardines and anchovies were regular fare for the citizens of Athens. They were sometimes sold fresh, but more frequently salted. A stele of the late 3rd century BCE from the small Boeotian city of Akraiphia, on Lake Copais, provides us with a list of fish prices. The cheapest was skaren (probably parrotfish) whereas Atlantic bluefin tuna was three times as expensive.[9] Common salt water fish were yellowfin tuna, red mullet, ray, swordfish or sturgeon, a delicacy which was eaten salted. Lake Copais itself was famous in all Greece for its eels, celebrated by the hero of The Acharnians. Other fresh water fish were pike-fish, carp and the less appreciated catfish.

Pictorial evidence of Roman fishing comes from mosaics.[10] At a certain time the goatfish was considered the epitome of luxury, above all because its scales exhibit a bright red color when it dies out of water. For this reason these fish were occasionally allowed to die slowly at the table. There even was a recipe where this would take place in garo, in the sauce. At the beginning of the Imperial era, however, this custom suddenly came to an end, which is why mullus in the feast of Trimalchio (see the Satyricon) could be shown as a characteristic of the parvenu, who bores his guests with an unfashionable display of dying fish.

In medieval times, seafood was less prestigious than other animal meats, and often seen as merely an alternative to meat on fast days. Still, seafood was the mainstay of many coastal populations. Kippers made from herring caught in the North Sea could be found in markets as far away as Constantinople.[11] While large quantities of fish were eaten fresh, a large proportion was salted, dried, and, to a lesser extent, smoked. Stockfish, cod that was split down the middle, fixed to a pole and dried, was very common, though preparation could be time-consuming, and meant beating the dried fish with a mallet before soaking it in water. A wide range of mollusks including oysters, mussels and scallops were eaten by coastal and river-dwelling populations, and freshwater crayfish were seen as a desirable alternative to meat during fish days. Compared to meat, fish was much more expensive for inland populations, especially in Central Europe, and therefore not an option for most.[12]

Modern knowledge of the reproductive cycles of aquatic species has led to the development of hatcheries and improved techniques of fish farming and aquaculture. Better understanding of the hazards of eating raw and undercooked fish and shellfish has led to improved preservation methods and processing.

The following table is based on the ISSCAAP classification (International Standard Statistical Classification of Aquatic Animals and Plants) used by the FAO for the purposes of collecting and compiling fishery statistics.[13] The production figures have been extracted from the FAO FishStat database,[14] and include both capture from wild fisheries and aquaculture production.

Demersal fish live and feed on or near the bottom of the sea.[15] Some seafood groups are cod, flatfish, grouper and stingrays. Demersal fish feed mainly on crustaceans they find on the sea floor, and are more sedentary than the pelagic fish. Pelagic fish usually have the red flesh characteristic of the powerful swimming muscles they need, while demersal fish usually have white flesh.

Bivalves, sometimes referred to as clams, have a protective shell in two hinged parts. A valve is the name used for the protective shell of a bivalve, so bivalve literally means two shells. Important seafood bivalves include oysters, scallops, mussels and cockles. Most of these are filter feeders which bury themselves in sediment on the seabed where they are safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some, such as scallops, can swim. Bivalves have long been a part of the diet of coastal communities. Oysters were cultured in ponds by the Romans and mariculture has more recently become an important source of bivalves for food.

Cephalopods are not protected with a shell. Cephalopod literally means head-foots, because they have limbs which appear to issue from their head. They have excellent vision and high intelligence. Cephalopods propel themselves with a water jet and lay down "smoke screens" with ink. Examples are octopus, squid and cuttlefish. They are eaten in many cultures. Depending on the species, the arms and sometimes other body parts are prepared in various ways. Octopus must be boiled properly to rid it of slime, smell, and residual ink. Squid are popular in Japan. In Mediterranean countries and in Britain squid are often referred to as calamari.[16] Cuttlefish is less eaten than squid, though it is popular in Italy and dried, shredded cuttlefish is a snack food in East Asia. See: Squid (food)Octopus (food).

Crustaceans (from Latin crusta, meaning crust ) are invertebrates with segmented bodies protected by hard crusts (shells or exoskeletons), usually made of chitin and structured somewhat like a knight's armour. The shells do not grow, and must periodically be shed or moulted. Usually two legs or limbs issue from each segment. Most commercial crustaceans are decapods, that is they have ten legs, and have compound eyes set on stalks. Their shell turns pink or red when cooked.Total for crustaceans:

Crabs are stalk-eyed ten-legged crustaceans, usually walk sideways, and have grasping claws as their front pair of limbs. They have small abdomens, short antennae, and a short carapace that is wide and flat. See: crab fisheries.

Clawed lobsters and spiny lobsters are stalk-eyed ten-legged crustaceans with long abdomens. The clawed lobster has large asymmetrical claws for its front pair of limbs, one for crushing and one for cutting (pictured). The spiny lobster lacks the large claws, but has a long, spiny antennae and a spiny carapace. Lobsters are larger than most shrimp or crabs. See: lobster fishing.

Krill are like baby shrimps, except they have external gills and more than ten legs (swimming plus feeding and grooming legs). They are found in oceans around the world where they filter feed in huge pelagic swarms.[20] Like shrimp, they are an important part of the marine food chain, converting phytoplankton into a form larger animals can consume. Each year, larger animals eat half the estimated biomass of krill (about 600 million tonnes).[20] Humans consume krill in Japan and Russia, but most of the krill harvest is used to make fish feed and for extracting oil. Krill oil contains omega-3 fatty acids, similarly to fish oil. See: Krill fishery.

Sea mammals form a diverse group of 128 species that rely on the ocean for their existence.[21] Whale meat is still harvested from legal, non-commercial hunts.[22] About one thousand long-finned pilot whales are still killed annually.[23] Japan has resumed hunting for whales, which they call "research whaling".[24] In modern Japan, two cuts of whale meat are usually distinguished: the belly meat and the more valued tail or fluke meat. Fluke meat can sell for $200 per kilogram, three times the price of belly meat.[25]Fin whales are particularly desired because they are thought to yield the best quality fluke meat.[26] In Taiji in Japan and the Faroe Islands, dolphins are traditionally considered food, and are killed in harpoon or drive hunts.[27]Ringed seals are still an important food source for the people of Nunavut[28] and are also hunted and eaten in Alaska.[29] The meat of sea mammals can be high in mercury, and may pose health dangers to humans when consumed.[30] The FAO record only the reported numbers of aquatic mammals harvested, and not the tonnage. In 2010, they reported 2500 whales, 12,000 dolphins and 182,000 seals. See: marine mammals as food, whale meat, seal hunting.

Sea turtles have long been valued as food in many parts of the world. Fifth century BC Chinese texts describe sea turtles as exotic delicacies.[31] Sea turtles are caught worldwide, although in many countries it is illegal to hunt most species.[32] Many coastal communities around the world depend on sea turtles as a source of protein, often gathering sea turtle eggs, and keeping captured sea turtles alive on their backs until needed for consumption.[33] Most species of sea turtle are now endangered, and some are critically endangered.[34] The FAO reports 1,418,975 crocodiles were harvested in 2010, but they do not record the tonnage.

Echinoderms are headless invertebrates, found on the seafloor in all oceans and at all depths. They are not found in fresh water. They usually have a five-pointed radial symmetry, and move, breathe and perceive with their retractable tube feet. They are covered with a calcareous and spiky test or skin. The name echinoderm comes from the Greek ekhinos meaning hedgehog, and dermatos meaning skin. Echinoderms used for seafood include sea cucumbers, sea urchins, and occasionally starfish. Wild sea cucumbers are caught by divers and in China they are farmed commercially in artificial ponds.[35] The gonads of both male and female sea urchins, usually called sea urchin roe or corals,[36] are delicacies in many parts of the world.[37][38]See: sea cucumber (food).

Jellyfish are soft and gelatinous, with a body shaped like an umbrella or bell which pulsates for locomotion. They have long, trailing tentacles with stings for capturing prey. They are found free-swimming in the water column in all oceans, and are occasionally found in freshwater. Jellyfish must be dried within hours to prevent spoiling. In Japan they are regarded as a delicacy. Traditional processing methods are carried out by a jellyfish master. This involve a 20 to 40 day multi-phase procedure which starts with removing the gonads and mucous membranes. The umbrella and oral arms are then treated with a mixture of table salt and alum, and compressed. Processing reduces liquefaction, odor, the growth of spoilage organisms, and makes the jellyfish drier and more acidic, producing a crisp and crunchy texture. Only scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food; about 12 of the approximately 85 species. Most of the harvest takes place in southeast Asia.[39][40][41]

Live food fish are often transported in tanks at high expense for an international market that prefers its seafood killed immediately before it is cooked. This process originally was started by Lindeye. Delivery of live fish without water is also being explored.[47] While some seafood restaurants keep live fish in aquaria for display purposes or for cultural beliefs, the majority of live fish are kept for dining customers. The live food fish trade in Hong Kong, for example, is estimated to have driven imports of live food fish to more than 15,000 tonnes in 2000. Worldwide sales that year were estimated at US$400 million, according to the World Resources Institute.[48]

If the cool chain has not been adhered to correctly, food products generally decay and become harmful before the validity date printed on the package. As the potential harm for a consumer when eating rotten fish is much larger than for example with dairy products, the U.S. Food and Drug Administration (FDA) has introduced regulation in the USA requiring the use of a time temperature indicator on certain fresh chilled seafood products.[49]

Fresh fish is a highly perishable food product, so it must be eaten promptly or discarded; it can be kept for only a short time. In many countries, fresh fish are filleted and displayed for sale on a bed of crushed ice or refrigerated. Fresh fish is most commonly found near bodies of water, but the advent of refrigerated train and trucktransportation has made fresh fish more widely available inland.

Long term preservation of fish is accomplished in a variety of ways. The oldest and still most widely used techniques are drying and salting. Desiccation (complete drying) is commonly used to preserve fish such as cod. Partial drying and salting is popular for the preservation of fish like herring and mackerel. Fish such as salmon, tuna, and herring are cooked and canned. Most fish are filleted prior to canning, but some small fish (e.g. sardines) are only decapitated and gutted prior to canning.

Seafood is consumed all over the world; it provides the world's prime source of high-quality protein: 14–16% of the animal protein consumed worldwide; over one billion people rely on seafood as their primary source of animal protein.[50][51] Fish is among the most common food allergens.

The UK Food Standards Agency recommends that at least two portions of seafood should be consumed each week, one of which should be oil-rich. There are over 100 different types of seafood available around the coast of the UK.

Oil-rich fish such as mackerel or herring are rich in long chain Omega-3 oils. These oils are found in every cell of the human body, and are required for human biological functions such as brain functionality.

Over 33,000 species of fish and many more marine invertebrate species have been described.[55] Bromophenols, which are produced by marine algae, gives marine animals an odor and taste that is absent from freshwater fish and invertebrates. Also, a chemical substance called dimethylsulfoniopropionate (DMSP) that is found in red and green algae is transferred to animals in the marine food chain. When broken down, dimethyl sulfide (DMS) is produced, and is often released during food preparation when fresh fish and shellfish are heated. In small quantities it creates a specific smell one associates with the ocean, but which in larger quantities gives the impression of rotten seaweed and old fish.[56] Another molecule known as TMAO occurs in fishes and give them a distinct smell. It also exists in freshwater species, but becomes more numerous in the cells of an animal the deeper it lives, so that fish from the deeper parts of the ocean has a stronger taste than species who lives in shallow water.[57] However, only a small number of species are commonly eaten by humans.

Fish and shellfish have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury, a highly toxic organic compound of mercury. Species of fish that are high on the food chain, such as shark, swordfish, king mackerel, albacore tuna, and tilefish contain higher concentrations of mercury than others. This is because mercury is stored in the muscle tissues of fish, and when a predatory fish eats another fish, it assumes the entire body burden of mercury in the consumed fish. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain amass body burdens of mercury that can be ten times higher than the species they consume. This process is called biomagnification. The first occurrence of widespread mercury poisoning in humans occurred this way in Minamata, Japan, now called Minamata disease.

A 2013 study by Oceana found that one third of seafood sampled from the United States was incorrectly labelled. Snapper and tuna were particularly susceptible to mislabelling, and seafood substitution was the most common type of fraud.[62] These practices can harm both the consumers' wallet and pose health risks. Another type of mislabelling is short-weighting,
[63] where practices such as overglazing or soaking can misleadingly increase the apparent weight of the fish. The detection of water retention agents helps identify the fraud and its origin.[citation needed]

Research into population trends of various species of seafood is pointing to a global collapse of seafood species by 2048. Such a collapse would occur due to pollution and overfishing, threatening oceanic ecosystems, according to some researchers.[64]

A major international scientific study released in November 2006 in the journal Science found that about one-third of all fishing stocks worldwide have collapsed (with a collapse being defined as a decline to less than 10% of their maximum observed abundance), and that if current trends continue all fish stocks worldwide will collapse within fifty years.[65] In July 2009, Boris Worm of Dalhousie University, the author of the November 2006 study in Science, co-authored an update on the state of the world's fisheries with one of the original study's critics, Ray Hilborn of the University of Washington at Seattle. The new study found that through good fisheries management techniques even depleted fish stocks can be revived and made commercially viable again.[66]

The FAO State of World Fisheries and Aquaculture 2004 report estimates that in 2003, of the main fish stocks or groups of resources for which assessment information is available, "approximately one-quarter were overexploited, depleted or recovering from depletion (16%, 7% and 1% respectively) and needed rebuilding."[67]

The National Fisheries Institute, a trade advocacy group representing the United States seafood industry, disagree. They claim that currently observed declines in fish population are due to natural fluctuations and that enhanced technologies will eventually alleviate whatever impact humanity is having on oceanic life.[68]

For the most part Islamic dietary laws allow the eating of seafood, though the Hanbali forbid eels, the Shafi forbid frogs and crocodiles, and the Hanafi forbid bottom feeders such as shellfish and carp.[69] The Jewish laws of Kashrut forbid the eating of shellfish and eels.[70] In the Old Testament, the Mosaic Covenant allowed the Israelites to eat finfish, but shellfish and eels were an abomination and not allowed.[71] In ancient and medieval times, the Catholic Church forbade the practice of eating meat, eggs and dairy products during Lent. Thomas Aquinas argued that these "afford greater pleasure as food [than fish], and greater nourishment to the human body, so that from their consumption there results a greater surplus available for seminal matter, which when abundant becomes a great incentive to lust."[72] In the United States, the Catholic practice of abstaining from meat on Fridays during Lent has popularized the Friday fish fry,[73] and parishes often sponsor a fish fry during Lent.[74] In predominantly Roman Catholic areas, restaurants may adjust their menus during Lent by adding seafood items to the menu.[75]